Endeavors to treat low back pain by means of a motion restoring intervertebral element have existed for many decades. Hoffmann-Daimler disclosed many such inventions in the Germany patent 2,263,842. These included ball and socket prostheses with single and/or dual articulations and with and without motion dampening elements. The clinical use of the device containing a ball supported by two opposing sockets extending from generally flat plates, was discussed in Hoffmann-Daimler's 1974 article published in Intervertebral Disk Displacement, Vol. 112, No. 4, August 1974. Hansen et al., U.S. Pat. No. 5,676,701, disclosed a low wear artificial spinal disc having opposing convex and concave contoured surfaces with a full 360 degree circumference. This allows for rotation but no translation. Yuichiro and Koichi, U.S. Pat. No. 5,899,941, disclosed a similar device but where the articulating surface is generally non-conforming to allow rotation and translational movement. This is similar to U.S. Pat. No. 6,113,637 by Gill et al. This artificial spinal disc incorporates a ball and trough type articulation with a substantially flat portion. Both the Yuichiro and Gill et al. patents describe devices which rely on point contact, a potential source of excessive wear debris.
The disclosed invention, in the form of first and second articulating components to be positioned between adjacent vertebral bodies, provides a more controlled rotation or in the alternative a controlled rotation with translation in one plane only, incorporating either surface to surface, or surface to line contact. As a result any translation away from the center in the one plane will produce device and joint distraction thereby providing a self-governing resistance to limit excessive translation.
The several disclosed embodiments of the invention provide two additional advantages over the more common artificial disc devices. The first is that the components or the majority of the parts of a composite components may be made of radio translucent or partially radio translucent material depending on the desired outcome. This greatly increases the ability for the device, surrounding tissue and bone to be evaluated using standard medical imaging techniques. The second advantage is that the parts of each composite component (for each articulating side) may be manufactured as one integrally formed unit. This reduces interconnected parts micro-motion and wear while increasing the system's ease of use.